1. Field Of the Disclosure
The present disclosure relates to a 3-dimensional (3D) graphics, and more particularly to, a method of perceptual 3D shape description and a method and apparatus for searching a 3D graphics model database established using the description method to retrieve the similar models to a query model.
2. Description of the Related Art
The number of 3D graphics objects to be managed has geometrically increased in response to the developments in 3D graphics technology and expansions in related technical fields. Therefore, there has been a need for techniques to efficiently store, manage, and reuse a number of 3D graphics objects.
According to MPEG-7, Shape3D is suggested and adopted as an international standard for 3D shape description and database searching. In general, 3D graphics models are expressed as polygonal meshes that consist of vertices and faces. Shape3D defines the shape spectrum of such polygonal meshes, which is the histogram of shape indices calculated on the whole surface of a mesh model.
However, some problems arise with Shape3D. First, the shape spectrum represents geometrical attributes of a local surface of a 3D object and cannot provide the overall, spatial information, thereby lowering shape discriminability. FIG. 1 illustrates an example of limited shape discriminability of Shape3D. In FIGS. 1(a) and (b) denote 3D objects, and (c) and (d) show the shape spectra of the objects (a) and (b), respectively. As is apparent from (a) and (b), ‘android’ model and ‘crocodile’ model have distinct shapes. However, their shape spectra are very similar to each other as shown in (b) and (d) of FIG. 1. A quantitative difference between the shape spectra of the ‘android’ and ‘crocodile’ models is merely 0.025981. In other words, when the ‘android’ object is used as a query for searching, the ‘crocodile’ object may be undesirably retrieved as one of the most similar objects, i.e., with a high similarity rank among the searched results. The searched shape has no similarity with the actual query shape. Therefore, using Shape3D is unsuitable for searching with a query by sketch or a query by editing, since there is no coherence between the actual shape and its shape spectrum.